Feed control for band saws



April 15, 1968 c. H. WHITMORE Re.-Re. 26,377

FEED CONTROL FOR BAND SAWS 5 Sheets-Sheet 1 Original Filed Feb. l5, 1960April 16, 1968 c. H. WHITMORE Re.-Re. 26,377

FEED CONTROL FOU BAN?) SAW' 5 Sheets-Sheet Original Filed Feb. 15. 1960l VWM April 16, 1968 c. H. wHl'rMoRE Re.-Re. 26,377

FEED CONTROL FOR BAND SAWS Original Filed Feb. l5, 1960 5 Sheets-SheetApril 16, 1968 c. H. wHl'rMoRE Re-Re 25,377

FEED CONTROL Fon BAND snws 5 Sheets-Shee` 4 original Filed Feb. 15. 19GoApril 16, 1968 c. H. wHn'MoRE Re.-Re. 26,377

FEED CONTRGL FOR BAND SAWS 5 Sheets-Sheet 5 Original Filed Feb. 15. 1960United States Patent O Matter enclosed in heavy brackets appears in theoriginal patent but forms no part of the first and this reissuespecification; matter printed in italics indicates the additions made bythe first reissue; matter enclosed in double heavy brackets [[1] appearsin the first reissue patent but forms no part of this reissuespecification; matter printed in bold face (except reference figures andclaim numbers) indicates the additions made by this reissue Thisinvention relates broadly to metal cutting tools, and refers moreparticularly to band saws and endless band-type cutoff saws like thatillustrated in the Crane et e al. Patent No. 2,898,669. The broadpurpose of the invention is two-fold-to provide an improved feed controlwhich assures a substantially uniform cutting rate despite changes inthe cross-sectional shape of the work being sawed, and to `maintainsubstantially uniform band loading by eliminating the effects of suchfactors as variations in the width of the band and lack of straightnessthereof, known as dog leg.

In cutoff saws, the pulleys about which the band or blade is trained arecarried by a head or frame which is mounted for up and down motion abovethe base of the machine. The work to be cut is supported on the base andthe cutting action takes place as the saw carrying frame descends.

In earlier `band-type cutoff machines, the saw carrying frame was simplyhinged to the base and as it swung down, the lower stretch of the bandcut through the work. In the cutoff saw of the aforesaid Crane et al.patent, it is the top stretch of the band which performs the cuttingaction, and the head or frame carrying the saw, instead of being hingedto the base, is slidably mounted upon vertical gulde posts whichconstrain it to a vertical translatory motion.

Hydraulic cylinders elevate the head or frame, and by regulating thedischarge of the fluid from the cylinders, its descent may becontrolled.

With a view toward preventing binding or hang-up of the frame on itsguide posts, a torque bar and linkage device was provided in the cutoffsaw of the aforesaid Crane et al. patent, to constrain both ends of theframe to move in unison. However, despite this and all other precautionsthat were taken to assure smooth uninterrupted descent of the frameduring sawing, hangup or unevenness in the descent of the frame wasinevitable. As a result, there were serious fluctuations in the loadupon the saw band or blade and highly objectionable variations in thecutting rate.

To appreciate this situation, it should be understood that the cuttingstretch of the saw band or blade is held in proper position to effectthe desired cutting action by saw guides located just ahead of the pointat which the saw enters the work and just beyond its point of emergencefrom the work. In addition to engaging the opposite sides or faces ofthe band and constraining it to its required vertical disposition, theseguides also include .so-called backup bearings which bear against theback edge of the band or blade, and apply downward feeding force on theband.

The backup bearings are, of course, mounted on the saw carrying head,and, in the past, were rigidly held with respect thereto, i.e. they hadno vertical motion independent of the frame or with respect thereto.Thus, any interference with the smooth descent of the head would have ndirect influence upon the feeding force applied to the band.

Another serious difficulty that was heretofore encountered in band-typecutoff saws, due to the manner in which the cutting stretch of the bandor blade was guided, resuited from the fact that saw bands inevitablyare not uniform in width, and also, despite all precaution to thecontrary, it is practically impossible to produce a saw band or bladewhich is absolutely straight. A certain amount of so-callcd dog leg isinescapable.

These inherent characteristics of band saw blades, plus the periodichang-up in the descent of the saw frame caused by binding at the guideposts or in the hydraulic cylinders, resulted in very serious variationsin loading upon the band and, of course, also upon the drive mechanismtherefor.

To illustrate, using the conventional prior art saw guides and backups,a variation of as much as 114 lbs. in the loading of the band wasobserved at one of the two guides, and 99 lbs. at the other, in onerevolution or cycle of the band. The present invention reduced thesevariations to only 28 lbs. and l5 lbs., respectively.

The present invention overcomes the indicated objections of the priorart through its use of an improved backup bearing structure. This backupbearing, instead of being secured in a fixed position, has a degree ofup and down movement with respect to the frame or head. In addition. itis resiliently or yieldably urged in the direction towards the saw bands0 as Io folow and sense the position of the band os it Hexe.: underreaction forces thereon during sawing, and to maintain a Substantiallyconstant sawing force on the band, compensating for dogleg andvariations in band width and for [momentary interruptions] anyinterference to smooth descent of the saw head by hang-up or binding atthe guide posts upon which the head or frame slides and in the hydrauliccylinders which regulate the descent of the head.

This is, of course, a significant and important advantage andimprovement over the art; but the present invention has an even greatervalue.

An important consideration in the economical and efficient operation ofa band sawing machine is the cutting rate at which the machine isoperated and which is dciincd as square inches of cut per unit of time.For each material, and also for each saw, there is an optimum cuttingrate at which performance of the machine is most economical and ecient.Substantial variations from this cutting rate, either upwardly ordownwardly, can bring about a material reduction in operating economy,having in mind not only blade life of the saw band itself but also suchconsiderations as the costs of labor and overhead. Consequently, it is[[exremely]] extremely desirable to maintain the cutting rate asuniformly as possible at the optimum rate.

While reduction in variations in band loading goes `a. long way towardachieving a uniform cutting rate, variations in the cross section of thework being cut are by far the most serious source of this difficulty.For instance, assume that a cut is being made through a piece of steeltwelve inches wide. For this particular material, and for the particularsaw blade being used, there is an optimum cutting rale. If now, thecross section of the work piece is such that as the cut deepens, thewidth of the piece abruptly changes to two inches, then obviously,unless the feeding force is also correspondingly reduced to ey'fct anappropriate adjustment in feed rale, thc cutting rate will be greatlyincreased and the saw no longer will be cutting at the optimum rate.

Of course, the machine could be manually readjusted,

but this is obviously objectionable if automatic compensation can behad. The present invention provides it.

Hence, it is one of the most important objectives of this invention toprovide a feed control for machine tools, and especially band saws andband-type cutoff saws, by which the feeding force is automaticallyadjusted whenever necessary to maintain a substantially uniform cuttingrate.

More specically, it is the purpose of this invention to provide acontrol for the feed of a band saw and band type cutoff saw, whereby thefeed rate is at all times corelated with the cross section of the workbeing cut.

Another object of this invention is to provide an improved band guideand feed control for band saws and band-type cutoff saws, which ischaracterized by a bodily movable control element which moves along thepath of the feeding motion of the machine and relative to the carrierfor the band, in strict conformance with such motion of the band orblade, and by its said motion directly controls the feed force in a wayto maintain a substantially uniform cutting rate despite changes incross section of the work being cut.

With the above and other objects in view which will appear as thedescription proceeds, this invention resides in the novel construction,combination and arrangement of parts substantially as hereinafterdescribed and more particularly dened by the appended claims, it beingunderstood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate two complete examples of thephysical embodiments of the invention constructed according to the `bestmodes so far devised for the practical application of the principlesthereof, and in which:

FIGURE 1 is a front view of a cut-off saw like that of Patent No.2,898,669, equipped with the improved saw guide and feed control of thisinvention, parts of the view being broken away, and the saw head beingshown raised and about to be lowered onto the work;

FIGURE 2 is a view essentially in vertical section through both guideunits, the one at the right being the control guide unit, i.e., beingthe unit which actually controls the descent of the saw head, said viewbeing at a scale considerably larger than that of FIGURE l;

FIGURE 3 is a detail sectional view through FIGURE 2 on the plane of theline 3-3, to illustrate particularly the side guides for the band orblade;

FIGURE 4 is a diagrammatic view of the entire control system,illustrating the same in the condition it is when the machine is inoperation sawing through a piece of work;

FIGURES 5, 6 and 7 are fragmentary diagrammatic views collectivelyillustrating how the control system achieves a substantially constantsawing or cutting rate, despite changes in the cross section of the workand the feeding force required; and

FIGURE 8 is a view more or less diagrammatically illustrating theapplication of this invention to a conventional band saw equipped with apower driven work feed table.

Referring now particularly to the accompanying drawings, and especiallyto FIGURES 1 and 2, the numeral `1f) designates the base of a band-typecutoff saw similar to that forming the subject matter of the Crane etal. Patent No. 2,898,659.

Mounted upon the base 10 for translatory vertical movement is a sawcarrying head or frame, designated generally `by the numeral 11. Thisframe is substantially U-shaped and has its arms disposed at oppositesides of a work supporting table 12 on the base to embrace the work Wset upon the table with the part thereof which is to be cut, in the workzone. Pulleys 13, at least one of which is power driven, are mounted onthe arms of the saw carrying frame or head, and trained about thesepulleys is an endless saw band or blade 14.

Since the cutoff machine illustrated in FIGURE 1 is like that of theaforesaid Crane et al. patent, it is the upper stretch of the band whichdoes the cutting. The lower stretch is at all times disposed beneath thework supporting table l2, even in the fully raised position of the head,in which position it is shown in FIGURE 1.

The frame or head y11 slides upon a pair of vertical posts 15 rigidlymounted on the frame; and hydraulic cylinders 16 having their ramsconnected to the base provide power means to elevate the frame or head.The posts are relatively [[relativlyll] widely spaced and the connectionbetween the frame 0r head and the posts is provided by a pair of widelyspaced bearings (not shown) on each arm of the frame, in which the postsare slidably received. In addition, in the hope of constraining theframe or head to exactly translatory motion, the opposite ends of theframe or head are connected with the base by a linkage and torque `bardevice 17, which has as its purpose to constrain both ends of the frameto move in unison as the frame is raised and lowered.

Theoretically, therefore, the frame or head should be incapable of anymotion other than true vertical translation, and its descent by gravity(no matter how slow) as well as its power actuated elevation should besmooth and uninterrupted. Hang-up or binding, either at the guide posts15 or in the hydraulic cylinders 16, should not occur. However, inpractice, this ideal condition does not exist. There is always a certainamount of hangup of the head as it descends during operation of themachine, and, because of it, the feed of the saw band through the work Wis not smoothly continuous. In the past this resulted in a seriouslyfluctuating band load, poor cutting accuracy and/ or poor surface nish.

The work W is held in position upon the base by cooperatinghydraulically actuated vice jaws 20, but since the present invention isnot concerned with the way these jaws are actuated or controlled, thisfeature of the machine has not been illustrated.

The axes of the pulleys 13, of necessity, are more nearly horizontalthan vertical, but the cutting stretch of the band must be vertical,that is, the band must have its faces exactly parallel to the directionof feed motion. lt follows, therefore, that this stretch of the bandmust lbe twisted and held exactly vertical as it enters and leaves thework zone. This is accomplished by a pair of right and left guide units,respectively designated by the numerals 22 and 23. The right-hand guideunit 22, as will be hereinafter more fully developed, controls thedownfeed of the saw head; the other unit 23, which is at the left sideof the work zone, may be considered as a follower, from the standpointof feed control.

The guide units 22 and 23 are mounted upon the saw head or frame 11 in amanner enabling them to be adjusted toward and from one another tonarrow or widen the work zone within the capacity of the machine. To somount the guide units, they are respectively fixed to arms 24 and 2S,which in turn are longitudinally slidably received in ways machined intobrackets 24'-25' on the frame or head. The machined ways are exactly inline with one another and parallel with the upper stretch of the band,so that in any position of adjustment the arms 24 and 25 hold the guideunits in position to constrain that part of the upper stretch of theband spanning the guide units to travel in a vertical plane, with itstoothed edge facing downwardly.

Clamping screws [wih] with hand wheels 26 are provided to clamp the arms24 and 25 in any adjusted position, which for best results is that atwhich the guide units are closely adjacent to tthe opposite sides of thework to be cut.

To the extent that the guide units 22 and 23 function to guide and holdthe cutting stretch of the saw band in a vertical plane, they aresubstantially identical. Thus, each has a pair of cooperating guideshoes 27 at the underside of its `body casting to slidingly engage theopposite sides of the saw band or blade and hold it rmly in its propervertical disposition as it travels through the cutting zone. FIGURE 3perhaps offers the best illustration of these side guides or shoes, butit should be understood that the specilic construction of these guideshoes forms no part of the present invention. Preferably, they are likethe guide shoes illustrated in FIGURE 6 of the copending applicationSerial No. 707,967, now Patent No. 2,934,106.

In addition to the guide shoes 27 which engage the sides of the band,the guide units 22 and 23 have backup bearings or rollers respectivelydesignated by the general reference characters 28 and 29, against whichthe back edge of the band bears, and by which the feeding force isapplied to the band. These backup bearings or rollers comprise spindles30-31, freely rotatably mounted in vertical bores 32-33 in the body[[castingl] castings of the two guide units. At their lower ends, thespindles have downwardly facing flat surfaced heads against which theback edge ofthe saw band bears. So that the spindles L will turn as theband passes under them, the engagement of the band with their downwardlyfacing surfaces is closer to the edges of the heads than their centers.The diameter of the heads is slightly less than that of the lower endsof the bores, which are somewhat reduced to provide upwardly facingshoulders 3233', so that the spindles together with their bearings maybe inserted into the bores from the top.

A distinguishing characteristic of the backup rollers is that theirspindles 30-31 have a degree of free axial motion in their respectivebores. The purpose of this limited axial freedom will be discussedhereinafter. At this point, the explanation will deal only with thestructure by which the backup rollers are mounted to be both freelyrotatable and axially movable within limits. Thus, the spindle of I.

each backup roller is supported in a pair of axially spaced upper andlower ball bearings 34 and 35, respectively. The outer races of thesebearings have a free sliding tit in their respective bores 32-33, and ineach case the outer race of the lower bearing seats upon the adjacentshoulder (32'-33) to define the limit of downward axial motion permittedthe backup rollers.

Interposed between the upper and lower bearings 34 and 35 are thrustbearings 36, the lower races of which have a thrust transmittingconnection with the inner races of the lower bearings 35, eitherdirectly or through a spacer; and since these inner races of thebearings 3S seat upon upwardly facing shoulders on the spindles, upwardend thrust imparted to the backup rollers is transmitted to the thrustbearings. The upper races of the t thrust bearings 36 are arranged totransmit upward end thrust to the outer races of the upper bearings 34through washers 38. To avoid engagement between the washers 38 and theinne-r races of the bearings 34, the upper faces of the washers arerelieved, as shown. Hence, upward end thrust imposed upon the backuprollers is transmitted through the thrust bearings 36 to the outer raceof the upper bearings 34.

The upward end thrust transmitted to the outer races of the upperbearings 34 is imparted to collars 40, which are freely axially movablein the upper enlarged portions 41 of the bores 32-33. A screw 42 isthreaded into each collar and locked in an adjusted position by a locknut 43, and in the uppermost end of each screw is a socket in which aball 44 seats to provide a thrust transmitting connection between eachspindle and a valve spool slidably mounted thereabove, this ballconnection accommodating any possible misalignment between the spindleand the valve spool. Since the valve spools of the two guide units arenot alike, either in structure or in function, they will be separatelydescribed.

The left-hand guide unit has a valve body 45 seated upon and secured tothe top of its body casting across the top of its bore 32; and coaxiallycommunicating with the bore 32 the valve body 45 has a cylindrical valveCit spool chamber 46. In this chamber is a slidably mounted valve spool47, the lower end of which is seated upon the ball 44. A spring 48confined between the upper end of the valve spool and the underside of aplug 49 threaded into the upper end of the chamber 46, yieldingly urgesthe valve spool 47 downwardly. Since the valve spool abuts the plug 49in its uppermost position, the threaded engagement of the plug 49 in theend wall of the chamber 46 provides an adjustment for the axial travelpermitted the spool 47 and the backup bearing or roller 29.

Three ports 50, 5I and 52 o-pen to the valve spool chamber 46; the port50 leading to the upper end of the chamber and the other two portsopening to the side of the chamber at axially spaced points.

The valve spool 47 controls communication between the ports to eitherdisconnect the port 50 from both of the other ports 51 and 52, orconnect the port 50 with one or the other of the ports 51-52. For thispurpose, the spool has an internal passage (or passages) 53 leading fromits upper end to a groove 54 encircling the spool medially of its ends.The width of this groove is less than the shortest distance between theside ports 51 and 52 so that in its neutral position the spooldisconnects the port 50 from both side ports. Slight endwise motion ofthe spool, however, connects either the side port 51 or the side port 52with the port 50, depending upon whether its endwise motion is upward ordownward.

The spool 47 serves not only as a movable valve member but also as apiston. Fluid pressure in the upper portion of the valve chamber 46exerts a downward force upon the top of the spool. This force is, ofcourse, in addition to that applied upon the spool by the spring 48, andordinarily is far in excess of the spring force, so that essentially itis the lluid pressure in the upper end of the chamber which determinesthe feeding force applied to the saw blade by the backup bearing orroller 29, and the magnitude of this Huid pressure determineswhere-between its upper and lower limitsthe backup bearing or roller 29will float with respect to the saw head. The value and purpose of thisfloating disposition of the backup bearing or roller 29 will be broughtout hereinafter.

At the right guide unit 22, which is the feed control unit, a valve bodyis seated upon and secured to the top of its body casting [[casingIl.This valve body 60 has a vertical bore 61 extending therethroughcoaxially of the bore 32. Slidably mounted in the bore 61 is a valvespool 62 which also serves as a piston. The medial portion of this spoolis reduced in diameter as at 63 to form an annular passage whichprovides controllable communication between ports 64 and 65, that opento the side of the bore 61 at vertically spaced points, the formerterminating in an annular chamber or cavity 64' which encircles thespool. A stem 66 projects axially downwardly from the spool 62 and intothe bore 32 to bear upon the adjacent ball 44.

A compression spring 67 reacting between the upper end of the valvespool 62 and the underside of a plug 68 threaded into the upper end ofthe `bore 61 biases the spool and the back-up bearing or roller 28towards their lowermost positions with respect to the saw head or frame,which positions are defined by the engagement of the bearing 35 with theshoulder 32'. The spring 67 exerts a biasing force on the saw band whichurges it in the same direction as the restoring force inherently in theband during sawing, which restoring force, of course, always tends loreturn the cutting stretch of the band to ils normal straight conditionfronti the cdgewise bowed condition to which it is fexed under thereaction force thereon during sawing. The upper limit of the permittedaxial motion of the valve spool and `backup bearing or roller is denedby the plug 68- and hence is adjustable.

In addition to the downward force applied by the spring 67, Huidpressure is also exerted on top of the valve spool 62. This uid pressureresults from having a port 69 in the upper end of the cylinder 61connected with a source of fluid under a pressure that can be adjustedlo suit sawing requirements [pressure through a port 69].

When the back-up bearing or roller 28 and the valve spool 62 oat intheir neutral or medial positions, the annular passage 63 is so disposedwith respect to the upper edge of the annular chamber or cavity 64' andthe port 65, that a predetermined relatively small degree ofcommunicaton is established between ports 64 and 65 and. as will behereinafter more fully described it is the extent of the communicationbetween these ports which controls the rate of descent of the saw heador frame.

The lower end portion of the bore 61 is divided by a barrier 70 intoaxially spaced cylinders 71 and 72. Functionally this barrier could bean integral pan of the body 60, but to allow for assembly, the barrieris a separate part secured in place by snap rings, as shown. The stem 66passes slidably through the barrier 70, and to prevent leakage suitableseats are provided, both at the wall of the bore 61 and at the stem 66.

A piston 73 is secured to the stem 66 to operate in the lower cylinder72, the securement again being preferably made by snap rings which, inthis case, engage the stem. The cylinders 71 and 72 contain fluid underpressure, and if the pressures within the two cylinders were equal, theywould have no effect, one way or the other, upon the lloating valvespool 62 and the backup bearing or roller 2S. On the other hand, if thepressure in the lower cylinder drops relative to that of the uppercylinder, the upwardly acting forces exerted on the valve Spool 62 willbe proportionately increased, and as a result, assuming that all otherforces remain unchanged, there will be an upward displacement of thespool. The significance of this feature will become clear as thedescription proceeds.

To enable the cylinders 71 and 72 to have uid pressure manifestedtherein, they have ports 74 and 75, respectively, through which thecylinders may be connected with a source of uid under pressure.

THE HYDRAULIC CONTROL SYSTEM AND ITS OPERATION The essential elements ofthe hydraulic feed control system are illustrated in FIGURE 4. As hereshown, a pump 80 takes oil or other suitable hydraulic uid from a tank81 and delivers it to the [system] port 69 in the top of the valve body60 at a pressure determined by the setting of an adjustable backpressure valve 82 in a by-pass line containing a restriction 82' andconnecting the discharge side of the pump with the tank. Preferably thisadjustable back pressure valve, and also a pressure gage connected inthe line ahead of the valve, are mounted on the control panel of themachine (not shown), since it is the setting of this valve whichdetermines the feeding force, and the back pressure valve is thus one ofthe controls which enables the operator to select a desired cuttingrate.

In FIGURE 4, the system is illustrated in the condition which obtainswhen the saw is in operation and cutting ythrough a piece of work. Thismeans that the main manual control valve of the system, indicatedgenerally by the numeral 87, is in its Operating position at which itestablishes communication between the hydraulic cylinders 16 and thetank 81. However, before cutting could begin, the saw head or frame hadto be elevated and, to do so, the control valve 87 was shifted to itsElevato position (shown in dotted lines in FIG URE 4), in which positionthe discharge side ot the pump was connected to the cylinders 16, theconnection from the valve to the cylinders being through a line 88 inwhich a check valve 89 is located. Since the valve 87 is connected withthe outlet of the pump upstream from the restriction 82', the fulloutput pressure of the pump will be available to lift the head Il. 0nthe other hand, as

will be readily appreciated, the restriction 82' prevents any signcantwaste of power since it limits the amount of pump output fluid which isbypassed to the tank Through the buck pressure valve 82.

As long as the control valve 87 is in its Elevate" position, thecylinders 16 not only support the entire weight of the saw head but boldit against descending. As soon as the valve 87 is shifted to itsOperating position, fluid flows from the [cylinder] cylinders and thesaw head begins to descend. The rate at which it descends depends uponhow fast the hydraulic tiuid can leave the cylinders 16 and this, inturn, depends upon the extent of the communication between the ports 64and 65 in the body 60 of the feed control unit, since these ports andthe annular chamber of cavity 64' to which the port 64 opens, areconnected in the return from the cylinders to the tank. This returncomprises the line 88, a line 90 which has an adjustable orifice 91connected therein for a purpose to be hereinafter described, thecylinder 61, a line 92, the valve 87, and a line 93.

Until the saw blade engages the work, the descent of the saw head and,hence, the velocity of the feeding motion is maximum, since at this timethe communication between the ports 64 and 65 is maximum as a result ofthe spool 62 being in its lowermost position. It is held in itslowermost position by the spring 67 and the tluid pressure manifested inthe upper end of the bore 61 [as] as a result of the port 69 beingconnected with the [pump] by-pass line downstream from the restriction82' through a line 84. The magnitude of this fluid pressure is, ofcourse, determined by the setting of the back pressure control valve 82.

Until the saw blade engages the work, the spool 47 in the left-handguide unit is also in its lowermost position, being held there by thespring 48. With the spool 47 in its lowermost position, the ports 50 and52 are communicated and, as a result of that communication, there is nouid pressure above the spool 47 nor in an accumulator 83 which is at all[time] times connected with the upper end of the bore 46, thecommunication between ports 50 and 52 having connected the accumulatorand the upper end of the bore 46 with the tank 81 through a line 99.

Obviously, in the case of a cut-0H saw of the type having a verticallymovable head, the weight of the head provides o force for in excess ofthat needed lo feed the sont through the work as the head descends. Thissubstantial force is resisted by the desired feed force between the sawblade and the work being sawecl, and which feed force is predeterminedby the setting of the valve 82,' hang-up or any other resistance tosmooth descent of the head; and the pressure of fluid in the cylinders16. By controlling the latter, which is done by throtlling or regulatingthe exhaust flow of fluid from the cylinders through the ports 64 and65, the cutting rate is kept courrant and at the desired valueregardless of substantial increases in the force which the head may haveto exert from time to time in overcoming resistance to smooth andunhinrlered descent thereof.

When the saw blade comes in to [contact] cutting engagement with thework, Such engagement imposes an upward reaction force upon the spool 62of the righthand guide unit which] This reaction force bows the sawblade and is thus opposed by the inherent restoring force of the blade.It is also opposed by [opposes] the downward biasing force exerted bythe spring 67 and the tluid pressure manifested in the upper end of thebore 6l and moves the spool] The spool thus moves upwardly in its boreuntil [the] all of these forces acting on the spool are in equilibrium.As the blade cuts through the work, the spool may at any time moverelative to the head in either direction parallel to the path of feedingmotion, and it does so in order to maintain a bias upon the saw bladewhich urges it in the direction toward the work with a force thatremains substantially unchanged so long as there is no change in thelength of the cut, as determined by the cross section of the work piece.Thus the feeding force is independent of feeding velocity of the sawhead, or more particularly the force which the head exerts in order toachieve the desired cutting rate despite opposition to smooth descent ofthe head. Constant cutting rate as predetermined by the adjustment ofthe back pressure control valve 82 is thus achieved because of thecapability of the support 28 for motion independently of the head and isdetermined by the adjustment of the back pressure control valve 82 whichregulates the pressure in the system].

To appreciate how the adjustment of the hydraulic pressure in the systemdetermines the feed force that is exerted upon the saw blade, it must berealized that the valve spool 62, in association with the ports itcontrols and the pressure of the spring 67, acts as a servo.

The purpose of the spring is to provide a force which, like therestoring force inherent n the saw blade, varies with the position ofthe blade and the spool, and this makes the device a proportionalcontrol. Thus, if the effect of pressure differential in the cylinders71 and 72 is discounted for the moment and for ease of explanation, theforces acting upon the spool 62 will be the hydraulic force and springforce on top of the spool and the 0pposing or reaction force of the sawband or blade against the backup bearing 28. If the latter foroe, i.e.the force of the band or blade against the backup bearing requires adownward force of 180 pounds to hold the spool at its control point ornormal position, a decrease in this reaction force to 179 pounds wouldallow the combined spring and hydraulic force to move the spool downwarduntil the spring force decreased by one pound, whereupon the spool wouldcome to rest. But in its new position the communication between theports 64 and 65 would be slightly greater than it had been, allowingmore uid to ow from the head cylinders 16, and thereby restore thedownward force t0 180 pounds. Had the band force (the upward or reactionforce) decreased to 178 pounds, the spring would have moved the spoolproportionally [further] farther and the orifice formed by thecommunication between the ports 64 and 65 would have been proportionallygreater.

This action always tends to drive the spool 62 back to its controlpoint, and in so doing, provides smooth recovery from changed loadconditions.

The location of the control point or normal position of the Valve spool62, thus is mainly a function of the reaction force upon the saw band[speed at which the head descends and the uid ows out of its cylinders16]. The total lioat" or motion of the spool permitted by its stops isonly 1,52 of an inch above and 1,@2 of an inch below its control point;and the variation in location of the control point [due to difference inthe quantity of fiuid passing through the orice (from port 64 to port65)] varies by only .005 or .006 of an inch.

The throttling effect upon the cw of fluid from the cylinders, ofcourse, retards the descent of the saw head, and hence the amount ofthrottling that takes place at ports 64 and 65 controls the velocity ofdescent of ythe head and the force under which the saw band is engagedwith the workpiece. The valving action at those ports is such as to soregulate the downward velocity of the head that it in effect follows theback-up bearing 28.

To adapt the machine to the cutting of dilierent metals and differentcross sectional shapes, the back pressure control valve 82 should beable to adjust the pressure in the [system] line 84 through a wide rangewhich, for pur poses of illustration, may extend from a high of S00 lbs.to a low of 20 lbs. No matter what the adjustment of the hydraulicpressure is, the backup bearings or rollers 28 and 29 and, of course,their respective valve spools, normally will float somewhere betweentheir upper and lower limits of movement with respect to the saw head orframe. As sawing conditions and [pressures in the lil system] forces onthe saw band vary, the backup bearings or rollers will seek dilierentnormal positions intermediate their limits.

If the work being sawed is of uniform width and uniform hardness, and ifit could be assumed that nothing would interfere with the smooth uniformgravity produced descent of the saw head, and if the width of the sawband were absolutely uniform and the band were entirely free fromdog-leg, the sawing operation would proceed uniformly at a predeterminedrate and neither backup bearing nor roller 28 or 29 would move either upor down from its normal or neutral position with respect to the saw heador frame. But, in practice, these ideal conditions do not exist.

Therefore, unless the possible variables are compensated, band loadingis apt to be erratic, cutting accuracy suffers, and the maintenance ofan optimum cutting rate is impossible. Variations in band width anddog-leg which heretofore produced a fluctuating band loading, arepractically entirely offset by the fact that the backup bearings orrollers 28 and 29 are yieldingly maintained in their normal positions.Thus the passage through the work zone of a two-wide portion of the bandwill merely cause the back-up bearings or rollers 28 and 29 to riseslightly, whereas a suddenly encountered decrease in band width willsimply allow the backup bearings or rollers to drop slightly. Dog-legwill be accommodated in the same way.

Such up and down floating of the backup bearings or rollers caused byvariation in band width and/or dog-leg, may be as much as twentythousandths of an inch, and as can no doubt be appreciated, the up anddown foating of the backup bearings or rollers takes place withoutmaterially increasing or decreasing the loading upon the teeth of theband or blade.

If a hard spot in the metal is encountered, or when the saw blade entersupon a wider cross section in the work, both backup bearings or rollersand their respective valve spools will be displaced upwardly from theirnormal position by the increased reaction of the work against the sawblade. The upward displacement of the valve spool 62 will decrease thecommunication between ports 64 and 65 and slow down the descent of thesaw head, but feeding force will be maintained. As the rate of descentof the head decreases, the downward bias upon the right-hand back-upbeating 28, exerted by the spring [69] 67 and the aforementionedinherent restoring force of the saw blade and hydraulic pressure in thecylinder 61 acting through the spool. 62, will maintain the feedingforce, [at least until the lower limit of relative motion between thebackup bearing or roller and the saw head is reached;] and at theleft-hand guide unit or follower, the feeding force will be similarlymaintained by the connection of the accumulator 83 and the valve spoolchamber 46 with the high pressure side of the system, as a result ofcommunication between the ports 50 and 51.

In the event descent ofthe saw head or frame is momentarily interruptedor slowed down by means other than the reaction of the work against thesaw blade, as, for instance, by binding or hang-up at the guide posts 0rthe hydraulic cylinders, the feeding force will be maintained by the[downward bias upon] forces urging the backup bearings [or rollers] andthe saw blade downwardly. Not only will this downward bias maintain thefeeding force but, `by increasing the communication between the ports 64and 65, the counterbalancing effect of the hydraulic fluid in thecylinders 16 will be decreased. This, of course, makes more of the forcederived from the weight of the head avai/able to move the headdownwardly against any forces that had momentarily retarded its motion,without imposing such increased force upon the saw band. As a result,the condition causing the momentary hang-up or binding will be [morereadily and more] quickly corrected.

In the foregoing description of the control system and its manner ofoperation, it has been shown how this invention maintains substantiallyuniform cutting and substantially uniform band loads, despiteinterference caused by varying band width, dog-leg, hard spots in themetal being sawed, and hand-up or binding which produces momentaryinterruptions in the descent of the saw head. But there is still anothercondition which will seriously affect the cutting rate. This isvariation in the cross section of the work piece being sawed.

A changing cross section or, more accurately, differences in the lengthof the cut being made, will affect the cutting rate unless the feed rateis appropriately adjusted. To help visualize this point, the work piece,where shown, is in the form of an H bar so placed that the cut is firstmade through one of the flanges, This placement of the work piece hasbeen chosen for illustrative purposes, despite the fact that in practiceit may be more logical to place the bar with its flanges vertical andgripped by the vise jaws.

If the cross of the H bar is the same as that of the web, for instance,each 2" x 12", it follows that if a uniform cutting rate is to kbemaintained, the saw must cut through each fiange in the same time thatit takes to cut through the web.

In each case, 24 square inches must be cut. Since the force required tofeed the saw through the work varies with the length of the cut beingmade, the feeding force needed to cut through the ange, as in FIGURE 5,must be greater than it is when the saw is cutting through the web, asin FIGURE 7, if the cutting rate is to be kept constant.

Conversely, as soon as the blade cuts through the top ange and beginsits cut down through the web, as shown in FIGURE 6, the feeding forcemust be abruptly reduced to a value below that of the force that hadbeen applied on the blade as it cut through the ange.

To effect the required adjustment of the feeding force is the functionof the cylinders 71 and 72 and the adjustable orice 91. The manner inwhich these elements function to effect their purpose will now bedescribed, and it is suggested that reference be had particularly toFIGURES 5, 6 and 7.

As already brought out, the hydraulic fluid leaving the cylinders 16flows through the adjustable orice 91 on its way to the port 64. The[static] pressure in the line downstream from the orice 91 is manifestedin the lower cylinder 72 since its port 75 is connected with the line 88downstream of the orifice. The static pressure upstream of the orificeis manifested in the upper cylinder 71, since its port 74 is connectedwith the line 88 upstream ofthe orifice.

Hence, the pressure in the upper cylinder 71 is not affected by the rateat which the uid leaves the cylinders 16, but the pressure in the lowercylinder 72 is affected by this rate. This follows from the fact that asthe velocity of the fluid owing through the orifice 91 increases, inconsequence of decreased restriction between ports 64 and 65, the[static] pressure downstream of the oritice decreases. [Any differentialin the pressures] The magnitude of the pressure differential in thecylinders 71 and 72 thus is a measure of the velocity of the feedingmotion or, in other words, the descent of the saw head.

As the saw blade breaks through the ange and begins its cut down throughthe web [(FIGURE 6) there is an abrupt reduction in the reaction of thework against the saw blade. With this reduction in reaction, the spool62 is forced downwardly in its cylinder 61 and, as a result, thecommunication between the ports 64 and 65 is increased. This allows theuid to ow from the cylinders 16 at a much more rapid rate and thusincreases the velocity of the flow through the orifice 91. As a resultof the increased liow through the orifice 91, the pressure in the lowercylinder is less than in the upper cylinder 71.

With this pressure dierential in the cylinders 71 and 72, a new upwardforce is applied upon the control spool sectional size and shape of eachflange 62. This added upward force shifts the spool 62 upwardly andthereby reduces the communication between the ports 64 and 65, which, inturn, proportionately reduces the rate of descent of the head] theresistance to sawing is suddenly diminished and there is a correspondingabrupt reduction in the reaction of the work against the saw blade.Hence, the saw is suddenly able to cut much faster and the spool 62 inthe cylinder 61 would move rapidly downwardly as a result thereof, to aposition such as seen in FIGURE 6, if it were not for the compensatingand modulating ecct of the cylinders 71 and 72. However, as soon as thespool begins to move downwardly from its position shown in FIGURE 5,fluid from the cylinders 16 exhausts through the orifice 91 and ports 64and 65 at an increased rate, to thus eect a proportionate decrease ofpressure in the lower cylinder 72 of the servo valve, while the pressurein its upper cylinder 71 remains the sante. This, of course, has theeect of adding upward bias on the spool of the servo valve and ofcorrespondingly resisting and controlling its downward motion. As aresult, the spool comes to rest in a new position, as for instance thatshown in FIG- URE 7, which is lower than that it had occupiedpreviously, to establish whatever degree of increased communicationbetween the ports 64 and 65 and whatever decreased pressure in the lowercylinder 72 is needed to bring all the forces acting upon the spool intoequilibrium. The net result is a substantially uniform cutting rate,despite the abruptly narrowed width of the work being cut.

The response and eect of the compensating cylinders 71 and 72 is mostpronounced at times when there are sudden increases or decreases inreaction forces on the saw band, such as occur during sawing of H beamsand other work pieces presenting abruptly changing cross sections to thesaw. Those skilled in the art will appreciate, however, that thecompensating cylinders can function under all sawing conditions,including those where the cross section of the work piece being sawedchanges very gradually to maintain a substantially uniform cutting rate.

Although for most materials no adjustment is needed at the orifice 91,it is preferable that the orifice be adjustable. lts adjustment isconveniently etfected by first setting the pressure control valve 82 forthe feeding force needed to achieve the optimum cutting rate for thegiven material and the appropriate saw blade, and then a test sample 12"wide and 2" thick (comparable to one of the anges of the H beam shown asthe work piece) is cut, with the saw traversing the 12" dimension. Afterthat section has been cut, the test piece is mounted edgewise. The oriceis now adjusted until the time required to cut through the piece in thisposition is the same as that needed to make the rst cut.

Since the backup bearing or roller 29 (the follower) moves toward itslowermost position with respect to the saw head when the reaction of thework against the saw tblade abruptly decreasesas when the saw bladebreaks through the frange and begins its cut through the web of the workpiece, and since this bearing or roller should oat medially of its upperand lower limits during the cutting, the pressure exerted upon its valvespool 47 should be reduced when the bearing or roller 29 moves downwardfrom its normal medial position. This is accomplished as a result ofcommunication between the ports 50 and 52.

When the ports 50 and 52 are connected by downward displacement of thespool 47 in its cylinder or chamber 46, some of the iluid in theaccumulator Hows out to the tank through a line 99 which leads from theport 52 and, as a result, the pressure above the spool 47 is reduced,allowing the backup bearing or roller 29 to resume its normal positionsomewhere between its upper and lower limits of motion.

Conversely, as already explained, when t-he backup bearing 29 is movedupwardly from its normal position 13 port 50 is communicated with port51 to send fluid under pressure from the pump to the accumulator 83 andthe upper portion of the cylinder 46, which Huid supplements thedownward biasing force of the spring 48 and returns the spool to itsnormal position.

THE MODIFIED EMBODIMENT OF THE INVENTION-FIGURE 8 In FIGURE 8, theinvention has been illustrated as applied to a conventional band saw inwhich the saw band or,blade 100 travels downwardly through the work zoneand the work W is carried by a horizontal work supporting table 101. Thework supporting table is mounted for horizontal traverse to feed workthereon to the saw blade. A hydraulic cylinder 102 mounted on the frameof the machine and having its ram 102' connected with the table,provides power means for advancing and retracting the table. Thus, byfeeding uid under pressure into one end or the other of the cylinder,the table may be advanced or retracted, and by controlling the iiow tothe cylinder, the feeding or cutting force may be regulated.

Hydraulic pressure is manifested at either end of the cylinder 102 byactuating a main control valve 103 from one extreme position to theother. With the valve 103 in the position shown, a pump 180 deliversiiuid at full pressure to a pressure line 104, and at the same timefluid pressure of a magnitude determined by the setting of an adjustableback pressure valve 182, is applied through a line 184 upon a valvespool 162. In this case also, the back pressure valve 182 is located ina by-pass line containing a restriction 182', and the control valve isconnected to the pump upstream from this restriction while the pressureline 184 leading to the servo valve is connected to the by-pass linedownstream from the restriction.

The pressure line 104 has a variable orifice 191 connected in it, andleads to port 164 of a cylinder 161 which is fixed with respect to theframe of the machine. The control spool 162 slides back and forth in thecylinder 161, to control communication between port 164 and a port 165,and as in the other embodiment of the invention, the spool is connectedwith a backup bearing or roller 129 to move in unison therewith. Thebackup bearing or roller supports the cutting stretch of the saw bladeagainst the thrust of the work thereon, and a spring 167 and thehydraulic pressure applied through line 184 yieldingly urges the spooland backup towards the saw blade.

Since the work has not yet engaged the saw blade (in FIGURE 8) the spool162 and the backup bearing or roller 129 are in their farthest advancedpositions, i.e., at the limit of their movement toward the saw blade.Maximum communication thus exists between ports 164 and 165, and as aresult, the full hydraulic force is applied through a line 105 to theleft-hand end of the cylinder 102. Immediately, the ram 102' begins tomove toward the right to advance the table 101 and feed the work Wagainst the saw band, the Huid discharging from the right hand end ofthe cylinder being led back to the tank 181 through a line 106, whichconnects that end of the cylinder with the tank through the valve 103.

As the work comes into engagement with the saw blade and applies itsreaction force thereon, the backup bearing or roller 129 and the controlspool 162 are moved toward the right until the reaction balances theinherent restoring force in the saw band, the yieldable force providedby the spring 167 and the hydraulic pressure in line 184 which together[urge] with the spring 167 urges the spool towards the saw blade, and,as a result, the degree of communication between the ports 164 and 165is reduced. With that reduction, as in the other embodiment of theinvention, the flow of hydraulic fluid through the duct 105 is reducedand the advance of the work supporting table 101 is proportionatelyslower.

inasmuch as the control spool 162 and the backup bearing or roller 129tioat in an intermediate position,

all of the advantages heretofore discussed are achieved in thisadaptation of the invention as well as in the other. Variations in bandwidth and dog-leg in the band or blade are accommodated by the freedomof the backup bearing to move forward and back, and any other conditionwhich would have an objectionable effect upon the band loading is eithereliminated or minimized.

Thus, if there is any reduction n the reaction force on the saw blade asa result of increased resistance to smooth traverse of thework-supporting table along its ways, greater force will be madeavailable to overcome such resistance and maintain the desired cuttingrate. This follows from the fact that the spool 162 in sensing theconsequent reduction in reaction force on the saw band, moves in thedirection to increase communication between the ports 164 and 165 andthereby effects relative worklfeeding motion between the work and thesaw band with whatever increased force may be needed to maintain thedesired cutting rate.

Likewise, when the cross section of the work being sawed or, moreaccurately, the [thickness of the piece being traversed by the sawblade, is less] length of the saw blade which is actually engaged withthe work is shorter, the feeding force is correspondingly reduced, sothat the cutting rate is maintained substantially constant.

This result is accomplished in the same way that it was in the otherform of the invention, Le., by means responsive to [a] change in thedifferential in pressure in cylinders 171 and 172. Cylinder 171 isconnected with the uid pressure system [downstream] upstream of theadjustable orilice 191 and the cylinder 172 is connected with the system[upstream] downstream of the orifice. Hence when the backup bearing 129and the control spool 162 [moves] begins to move to the left as thereaction of the work against the blade suddenly decreases, [and] thecommunication between ports 164 and 165 is correspondingiy enlarged[allowing the fluid] As fluid begins to iiow through the orice 191 at afaster rate, the resulting drop in pressure in the cylinder 172increases the pressure diiferential in the cylinders 171 and 72 andcauses force to be exerted [acts] upon the control spool 162 to[proportionately reduce the communication between the ports and therebydiminish the feeding force] resist motion of the spool beyond a positionestablishing whatever degree of communication between the ports 164 and165 is necessary to bring all of the forces acting upon the spool intoequilibrium and thus establish the reduced feeding force needed tomaintain constant cutting rate.

It will be noted that in the embodiment of the invention shown in FIGURE8, only the control backup bearing or roller has been illustrated. Thisbackup is part of the upper band guide unit. There is, of course, alower guide unit below the table 101, and its backup bearing or rollermay be of the oating construction as in the follower unit 23 of theother embodiment of the invention, or it may be a conventional fixedback-up. In fact, most of the advantages of the invention would berealized even in the cutoff saw embodiment of the invention, if thebackup bearing or roller 29 of its follower unit were fixed, that is,not capable of floating up and down.

When the work has been sawed and the table is to be retracted, the valve103 is actuated to feed the full pump pressure to the righthand end ofthe cylinder 102, and to enable rapid traverse of the table on itsreturn stroke, a check valve 189 [[conects]] connects line 105 with line104. This allows the fluid to by-pass the control unit.

From the foregoing description taken in connection with the accompanyingdrawings, it will no doubt be apparent to those skilled in this art thatthis invention constitutes a very significant improvement in band sawsand band-type cutoff machines and, for that matter, machine toolsgenerally, having comparable functions; especially because of itsattainment of a constant cutting rate despite changing conditions which,ordinarily, would cause the cutting rate to uctuate seriously from theselected optimum rate. It will also be apparent that the inventionpossesses the very important advantage of maintaining a substantiallyconstant feeding force between the saw teeth and the work piece beingsawed while sawing a uniform cross section, regardless of variations inband width and other conditions which heretofore have caused erraticband loading. The net result accomplished by the inven tion, therefore,is:

(l) Longer band life-since all parts of the band receive the same amountof wear.

(2) Higher cutting rates without overloading the saw teeth.

(3) Straighter cuts at high cutting rates.

(4) Better finish of the work piece with respect to greater accuracy andsmoothness of cut.

What is claimed as my invention is:

1. In a `machine tool of the type having a work supporting element and atool carrier element with a cutting tool thereon, one of said elementsbeing mounted for feeding motion relative to the other and said machinehaving force producing means for effecting such feeding motion of saidone element; means carried by the tool carrier element to guide thecutting tool for limited back and forth motion relative to the toolcarrier element [along a] in the path [parallel to the direction] offeeding motion; tool supporting means movably carried by said toolcarrying element and mounted to engage the tool and [through whichfeeding force is applied to the tool] to move therewith relative to thetool carrier element; biasing means reacting between the tool carrierelement and the tool supporting means to urge the [latter] tool in[said] the direction [relative to the tool carrier element] toward thework with a predetermined force which is [independent of] unaected bythe position of the tool supporting means with respect to the toolcarrier element; means reacting between the tool carrier element and thecutting tool to provide a supplemental biasing force that modifies[[and]] said predetermined biasing force and cooperates therewith toprovide a net feeding force under which the tool and a work piece on thework supporting element are engaged, and which supplemental biasingforce so varies with changes in the position of the tool relative[[realative]] to the tool carrier element that the net feeding forcedecreases with movement of the tool relative to said tool carrierelement in said direction and increases with such movement in theopposite direction; control means operatively connected with the cuttingtool and responsive to its movement relative to the tool carrier elementin each direction along said path; and force regulating means[operatively connected with said means for effecting feeding motion andupon which the control means acts to so regulate the velocity of thefeeding motion of said one element as to increase said velocity when thecutting tool moves] for said force producing means' and cooperating withsaid control means to cause feeding motion to be eected by the forceproducing means under increasing force in consequence o] response of thecontrol means to movement of the cutting tool in said direction relativeto the tool carrier element and to [decrease said velocity when thecutting tool moves] cause feeding motion to be eected by the forceproducing means under decreasing force in consequence of response of thecontrol means to movement of the cutting tool in the opposite directionrelative to the tool carrier element, whereby the net feeding forceunder which the tool and a work piece on the work supporting element areengaged can be maintained substantially uniform.

2. The machine tool set forth in claim 1, further characterized by thefact that: said first designated biasing means comprises Huid pressureresponsive means connected between the tool supporting means and thetool carrier element; and means for applying a predetermined fluidpressure to said tiuid pressure responsive means.

3. The machine tool set forth in claim 1 wherein said means providingthe supplemental biasing force reacts between the tool carrier elementand the tool supporting means. t

4. The machine tool set forth in claim 3, wherein said means providingthe supplemental biasing force is a spring.

5. The machine tool set forth in claim 2 wherein said means providingthe supplemental biasing force is a spring reacting between the toolcarrier element and the tool supporting means.

6. A machine tool of the type having a work supporting element and atool carrier element with a cutting tool thereon, one of said elementsbeing mounted for feeding motion relative to the other, and the toolbeing movable relative to the carrier along the path of feeding motion,said machine tool being characterized by means for engaging the cuttingtool with a workpiece carried by the work supporting element under afeeding force having a magnitude which is so controlled as to maintainthe cutting rate of the tool through the workpiece substantiallyconstant despite variations in cross sectional shape of the workpiece,said means comprising: force transmitting means movably carried by thetool carrier element, engaging the cutting tool and supporting the same,said force transmitting means being [mounted for limited motion]constrained to move in unison with the cutting tool relative to the toolcarrier element along [a] said path [substantially parallel to thedirection of feeding motionl, means operatively connected with the forcetransmitting means for applying thereto a biasing force which urges thetool in the direction [toward the work supporting element] to oppose thereaction force on the tool during cutting and the magnitude of whichbiasing force varies with the position of the force transmitting meansand the cutting tool along its path of motion decreasing withbias-produced motion [in said direction] of the force transmitting meansrelative to the tool carrier element; feed motion producing meansconnected with said elements for causing said one element to move [at a]under controllably variable [rate] force and [[a]] at derent rates;regulating means for controlling said feed motion producing means tovary the [rate of] force by which feeding motion of said one element iseffected in accordance with change in the magnitude of the biasing forcebeing exerted on the tool by the force transmitting means and broughtabout by change in said reaction force on the cutting tool, saidregulating means comprising structure operatively associated with thefeed motion producing means and the force transmitting means andresponsive to the position of the latter and the cutting tool along itspath of motion to cause the [rate of] ,force by which feeding motion ise'fcted to increase with bias produced motion of the force transmittingmeans [in said direction] relative to the tool carrier element, and todecrease with its reaction produced motion [in the opposite direction],and compensating means operatively associated with the feed motionproducing means and the force transmitting 4means [to so modify thebiasing force upon the force transmitting means as to decrease saidforce with increasing feed rates and increase said force with decreasingfeed rates] and responsive to movement of the force transmitting meansbrought about by sudden changes in said reaction force upon the cuttingtool to decrease the biasing effect upon the force transmitting meanswhenever said reaction force on the cutting tool suddenly decreases andthereby accordingly prevent said regulating means from eecting acorrespondingly large increase in the force by which feeding motion iseected by said feed motion producing means, and to [[ncrcasing]]increase the biasing effect upon the force transmitting means wheneversaid reaction force on the cutting tool suddenly increases and therebyaccordingly prevent said regulating means from eecting a correspondinglylarge reduction in the force by which feeding motion is effected by saidfeed motion producing means.

7. The machine tool of claim 6, wherein said compensating meanscomprises: countcrbiasing means reacting between the tool carrierelement and the force transmitting means to provide biasing force whichopposes that exerted upon the force transmitting means by the rstdesignated biasing means; and means operatively associated with the feedmotion means and with said counterbiasing means for increasing the forceexerted by the latter with increasing feed rates and decreasing saidforce with decreasing feed rates.

8. In a band type sawing machine having a work supporting element and atool carrier element, one of said elements being mounted for feedingmotion relative to the other, the tool carrier element carrying spacedapart pulleys with an endless saw blade trained about them, one stretchof the saw blade being the cutting stretch and passing lengthwisethrough the work zone of the machine zo eect sawing as feeding motion isimparted to said one element, means for so controlling the magnitude ofthe feeding force which the cutting stretch of the blade exerts againsta work piece on the work supporting element as to maintain the cuttingrate substantially constant, said means comprising: a back-up; meansmounting the backup on the tool carrier element in [supporting] forcetransmitting engagement with the cutting stretch of the saw blade at oneside of the work zone and for limited back and forth motion relative tosaid [[elment]] element along a path substantially parallel to the pathof feeding motion; biasing means reacting between the tool carrierelement and the back-up to urge the back-up and the cutting stretch ofthe saw blade relative to the tool carrier clement in a directiontowards a work piece on the work supporting element with a force thatopposes reaction force on the blade during sawing and varies inmagnitude with the position of the back-up along its path, decreasingwith relative motion of the back-up in said direction; a movable controlmember connected with the backup to move in correspondence therewith;feed motion producing means connected with said [elements for causingsaid] one element to [have] impart thereto feeding motion at acontrollably variable rate and to c ect such feeding motion underregulatable force; [feed rate] control means connected with the movablecontrol member to be responsive to the position thereof and operativelyassociated with the feed motion producing means for [so] controlling the[rate of] force by which feed motion is eected in accordance with theposition of the control member so as to provide for increasing [feedrates] said force with bias-produced motion of thc back-up in saiddirection and for decreasing [feed rates] said force withreaction-produced motion of the back-up in the opposite direction; meansoperatively associated with the feed motion producing means forproducing an output of a magnitude which varies with the rate of feedmotion; and compensating means connected with said output producingmeans to be [[respective]] responsive to its output and operativelyassociated with the back-up to so modify the eect of said biasing forcethereon as to decrease said [force] eect with increasing feed rates andincrease said [force] eecz with decreasing feed rates.

9. The structure of claim 8 further characterized by: a second back-upengaging the cutting stretch of the saw blade at the other side of thework zone; means mounting said second back-up on the tool carrierelement for limited back and forth motion relative to said element alonga path substantially parallel to the path of feeding motion; variablebias means operative to react between the tool carrier element and saidsecond back-up to urge the latter in the direction towards a work pieceon the work supporting element; and bias control means responsive to theposition of the second back-up along its said path and operativelyassociated with the variable bias means to so regulate the magnitude ofthe biasing force exerted thereby as to increase said biasing force withmotion of the back-up in said direction and decrease said biasing forcewith motion of the back-up in the opposite direction, to thus maintainthe forces biasing the blade toward a work piece substantially the sameat both sides of the work zone.

10. The structure of claim 9, further characterized by the fact that:said variable bias means comprises hydraulic cylinder and piston meansoperatively associated with the second back-up to apply thereto abiasing force proportional to the pressure of hydraulic fluid in saidcylinder and piston means, a pressure accumulator so connected with thecylinder and piston means that the pressure of fluid in the lattercorresponds to the pressure in the accumulator, and means providing asource of hydraulic fluid under substantially constant pressure; andwherein said bias control means comprises valve means connected with thesecond back-up to move in unison therewith and so connected with theaccumulator, said hydraulic fluid source and a vent as to permit fluidto flow from said source into the accumulator when the second back-upmoves in said opposite direction from a predetermined position andpermits fluid to ow from said accumulator to the vent when the back-upmoves in said direction from said predetermined position.

l1. The structure of claim 8, further characterized by the fact that thcfeed motion means comprises hydraulic cylinder means and means toconnect said cylinder means with a iluid pressure source; and by thefact that the compensating means comprises a pair of [pressureresponsive force producing] force applying devices connected together inopposed relation to produce a resultant output force and connected withthe control member to impose said output force thereon; and further bythe fact that said output producing means comprises a hydraulic lineconnecting one of Suid devices with the hydraulic cylinder means so thatsaid device is responsive to the static pressure in the cylinder meansand imposes the force thereof upon the control member in the directionto resist its motion with the back-up under the nfuence of the biasingmeans acting on the latter, a second hydraulic line connected with thehydraulic cylinder means and through which fluid flows during feedingmotion of said one element at a velocity depending upon the velocity ofthe feeding motion of said one element, a restricted orifice in saidsecond line so that the [static] pressure downstream of said orifice isproportionately less than that obtaining in the cylinder means as thevelocity of the flow through said second line increases, and meansconnecting the other [pressure responsive] device with the second linedownstream of said orifice so that the resultant output of said opposed[pressure responsive force producing] devices is a measure of thevelocity of the feeding motion of said one element.

12. The structure of claim 8, further characterized by the fact that themeans mounting the back-up on the tool carrier element comprises acylinder fixed with respect to said element with its axis in line withthe path of feeding motion, the back-up having a part slidably receivedin the cylinder, the control member also being slidably received in thecylinder and connected to said part of the back-up to move in unisontherewith; and the means providing the biasing force acting on thebackup comprising a source Of fluid pressure, duct means connecting theend of the cylinder remote from the backup with the fluid pressuresource, and piston means on said control member and disposed in thecylinder so that fluid pressure manifested in the cylinder imparts abiasing force upon the connected control member and back-up.

13. The structure of claim 12, further characterized by the fact thatthe means whereby feeding motion of said one element is effectedcomprises hydraulic actuating cylinder means and duct means connectedwith the same through which fluid can iiow into and out of the hydraulicactuating cylinder means; and by the fact that the means by which the[rate of] force with which feeding motion is regulated comprises inletand oude! ports in said cylinder in which the control rncmbet slides,said ports being connected in series with said duet means, and means onthe control member to adiust communication between said ports toincrease the communicaion upon movement of the control member inresponse to the biasing force and decrease the communication uponmovement of the control member in response to reaction [the the feedingmeans] produced motion of the control member to thereby controi the rateat which iiuid ilows through said duct means.

14. The structure of claim 12 wherein said source of uid pressureprovides a [pressure] biasing force which is substantially uniform,further characterized by a spring reacting between the tool carrierelement and the back-up to supplement the biasing force of the uidpressure manifested in said cylinder and provide for variation in themagnitude of tbe biasing force on the back-up in accordance with itsposition.

15. In a machine tool of the type having a carrier with a cutting toolthereon, and having regulatable force applying means for effectingrelative feeding motion between the tool carrier and' a workpiece beingcut by the tool, characterized by the following.' that the cutting toolis mounted for limited back and forth movement with respect to thecarrier along the path of relative feeding motion; that the cutting toolis biased to resist such relative movement in one direction with a forcethat opposes and balances reaction force on the cutting tool when thelatter is engaged with a work piece under a feed force of apredetermined and desired value, and which biasing force is derived inpart from a Huid pressure source that is unaffected by changes in theposition of the cutting tool with respect to the carrier; and thatcontrol means connected with the cutting tool senses its position withrespect to the carrier and cooperates with the force applying means toregulate the force by which said relative feeding motion is effected inaccordance with the position of the cutting tool with respect to thecarrier, so as to increase said last named force in response to anyslight bias-produced motion of the cutting tool with respect to thecarrier whenever feed force drops below said predetermined value, and todecrease the force under which relative feeding motion is effected inresponse to motion of the cutting tool with respect to the carrier underthe increasing reaction force that restores said balance betweenreaction and biasing forces.

16. In o machine tool of the type having a carrier with a cutting toolthereon, and having regulatable force applying means for effectingrelative feeding motion between the tool carrier and a work piece beingcut by the tool, characterized by the following: that the cutting toolis mounted for limited back and forth movement with respect to thecarrier along the path of relative feeding motion; that the cutting toolis biased to resist such relative movement in one direction with a forcethat opposes and balances reaction force on the cutting tool when thelatter is engaged with a work piece under a feed force of apredetermined and desired value, and which biasing force is derived inpart from a fluid pressure source that is unaffected by changes in theposition of the cutting tool with respect to the carrier; and thatcontrol means connected' with the cutting tool senses its position withrespect to the carrier and cooperates with the force applying means toregulate the force by which said relative feeding motion is effected inaccordance with the position of the cutting tool with respect lo thecarrier, so as to modify said last named force as needed to maintain thefeed force at its predetermined desired value.

17. In a machine tool of the type having a work supporting element, atool carrier element, and a cutting tool thereon which can move back andforth. along a defined path relative to the tool carrier element and' ismoved in one direction along said path, relatjvie to vthe tool carrierelement, in consequence of the reaction force resulting from engagementof the cutting tool with a work piece on the work supporting element:means on the tool carrier element for opposing reaction force on thecutting tool with a biasing force [[that]] derived in part from a fluidpressure source that is unaffected by the position of the ycutting toolwith respect to the carrier and which biasing force balances reactionforce of a predetermined value when the cutting tool occupies a positionalong said path corresponding to a desired feed force with which thecutting tool is engaged with a work piece on the work supportingelement; regulatable force applying means to e'ect relative feedingmotion between the cutting tool and o work piece on the work supportingelement; and control means carried by the tool carrier element andconstrained to back and forth movement relative thereto in unison withthe cutting tool as the latter moves in consequence of change inreaction force thereon either above or below said predetermined value,said control means governing said force applying means and cooperatingtherewith during its motion with the cutting lool to effect relativefeeding motion between the cutting tool and a work piece on the worksupporting element under forces which vary inversely with increase ordecrease in reaction force from said predetermined value, whereby saidforce applying means can be continuously adjusted during cutting and thenet feeding force under which the cutting tool is engaged with a workpiece on the work supporting element can be maintained at asubstantially constant value.

I8. In a machine tool of the type wherein a cutting tool eects cuttingof a work piece in consequence of relative feeding motion between thecutting tool and the work piece. a work support; a carrier on which thecutting7 tool is mounted for movement relative thereto in eitherdirection along a path parallel to the path of feeding motion, saidcutting tool being movable relative to the carrier in one directionalong said path in consequence of reaction force resulting from cuttingengagement of the tool with a work piece on the work support, and beingbiased with a force [[thatj] derived in part form a Huid pressure sourcethat is unaffected by changes in the position of the cutting tool withrespect to the carrier and which force resists such relative movement ofthe cutting tool in said one direction and yieldingly maintains the samein a normal cutting position when reaction force thereon is at apredetermined value corresponding to a desired feed force under whichthe cutting tool is engaged with a work piece on the supp-ort;regulatable force applying means to effect said relative feeding motionwith a force that can greatly exceed said predetermined reaction force;and control means for sensing slight deviations of the cutting tool fromsaid normal position thereof and for adjusting said regulatable force incorrespondence therewith, said control means being operable to increasesaid regulatable force in consequence of bias produced relative movementof the cutting tool in the opposite direction from said normal positionthereof whenever reaction force on the cutting tool drops' below saidpredetermined value, and to decrease said regulatable force incorrespondence with return relative motion of the cutting tool to saidnormal position thereof, whereby the feed force under which the cuttingtool is engaged with a work piece on the work support can be maintainedat a substantially constant value despite such interference withrelative feeding motion as might require the latter to be effected underforces greatly exceeding the desired feed force.

[[19. The machine tool of claim 18 wherein: the cutting tool isresiliently flexible, and the bias thereon includes bias producing meanswhich is independent of said regulatable force applying meansl] [[20.The machine tool of claim I9, wherein: said bias producing means exertsa constant biasing force upon the cutting tool.]]

2l. A machine lool of the type having a work supporting element and atool carrier element with a cutting tool thereon, one of said elementsbeing mounted for feeding motion relative to the other, and the toolbeing movable relative to the carrier along the path of feeding motion,said machine tool being characterized by means for engaging the cuttingtool with a workpiece carried by the work supporting element under afeed force having a magnitude which is so controlled as to maintain thecutting rate of the tool through the workpiece substantially constantdespite variations in cross sectional shape of the workpiece, said meanscomprising: force transmitting means movably carried by the tool cartierelement and bearing against the cutting tool so as to receive thereaction force imposed thereon during cutting, said force transmittingmeans being constrained to move in unison with the cutting tool relativeto the tool carrier element along said path; yieldable means operativelyconnected with the force transmitting means for applying thereto abiasing force which acts on the cutting tool in opposition to saidreaction force with an effectiveness that varies directly with suchincrease or decrease in said reaction force as eects any movement of theforce transmitting means and the cutting tool along said path of motion;feed motion producing means connected with said elements for causingsaid one element to move under control/ably variable force and atdifferent rates; regulating means operatively associated with the forcetransmitting means and said feed motion producing means to vary theforce which the latter applies to said one element in accordance withsaid movement of the force transmitting means and the cutting tool, saidregulating means being responsive to bias-produced movement of the forcetransL mitting means to cause an increase in the force by which feedingmotion is eected, and being responsive to reaction-produced movement ofthe force transmitting means to cause a decrease in said force; andcompensating means operatively associated with the feed motion producingmeans and the regulating means and responsive to biaslproduced movementof the force transmitting means to limit such movement thereof at timeswhen there is a sudden decrease in reaction force upon the forcetransmitting means and thereby accordingly limit increase in the forceby which feeding motion is effected by said feed motion producing means,and responsive to reaction-produced motion of the force transmittingmeans to limit such motion thereof at times when reaction force on thecutting tool suddenly increases, and thereby accordingly limit decreasein the force by which feeding motion is effected by said feed motionproducing means.

22. A machine tool of the type which is characterized by a tool carrier,by regulatable force applying means for eecting relative feeding motionbetween the carrier and a workpiece to be cut, and by a cutting tool onthe carrier which is maintained in a normal position with respect to thecarrier as long as feed reaction force on the cutting tool, which isopposed by an equal biasing force reacting between the cutting edge ofthe tool and the carrier, is at a predetermined value, said cutting toolbeing movable relative to the carrier in Opposite directions along thepath of relative feeding motion under the influence of one or the otherof said forces in correspondence with changes in feed reaction. force,and said machine tool being further characterized by: regulating meansfor adjusting the force with which said relative feeding motion iseffected by the force applying means; a control element for saidregulating means movably carried by the carrier to follow and sense theposition of the cutting tool relative thereto, said control elementbeing responsive to said relative movement of the cutting tool resultingfrom changes in feed reaction force thereon and cooperating with theregulating means and the force applying means to vary the forceeffecting said relative feeding motion inversely with changes in feedreaction force from said predetermined value thereof; and compensatingmeans operatively associated with the control element and the cuttingtool and responsive to a function of the rate at which relative feedingmotion is effected to so modify the eect of said biasing force as todecrease said e'ect whenever a decrease in feed reaction force tends toresult in an increase in the rate of relative feeding motion to a valueabove a predetermined desired rate, and to increase said effect wheneveran increase in feed reaction force tends to result in a decrease in therate of relative feeding motion to a value below said predeterminedrate.

23. A machine tool of the type which is characterized by a tool carrier,by regulatable force applying means for effecting relative feedingmotion between the carrier and a work piece to be cut, and by a cuttingtool on the carrier which moves relative thereto along the path offeeding motion in either direction from a position it occupies duringcutting at a selected rate and at which time reaction force on thecutting tool is at a predetermined value corresponding to the feed forcewith which the cutting tool must be engaged with a work piece to achievethe selected cutting rate, in consequence of change in said recationforce above and below said predetermined value, and furthercharacterized by: regulating means for adjusting the force with whichrelative feeding motion is effected by the force applying means; acontrol element for said regulating means movably carried by the Carrierto follow and sense the position of the cutting tool relative thereto,said control element cooperating with the regulating means and the forceapplying means to effect said relative feeding motion with forces thatvary inversely with increase and decrease in reaction force from saidpredetermined value thereof, in consequence of the movement of thecutting tool resulting from such change in reaction force; andcompensating means operatively associated with the force applying meansavid the control element to modulate the eect on the latter of movementof the cutting tool under the influence of sudden substantial changes inreaction force from said predetermined value thereof.

24. A machine tool of the type which is characterized by a tool carrier,by regulatable force applying means for effecting relative feedingmotion between the carrier and a workpiece to be machined, and by acutting tool on the carrier which is movable relative thereto inopposite directions along the path of relative feeding motion inconsequence of increase and decrease in feed reaction force on thecutting tool, and said machine being further characterized by: firstinstrumentalities associated with the cutting tool and with the forceapplying means and operative in consequence of relative movement of thecutting tool resulting from said changes int feed reaction force thereonto regulate the force by which said relative feeding motion is effectedinversely with said changes in feed reaction force; secondinstrumentalities associated with the force applying means andresponsive to a function of the rate at which said relative feedingmotion is effected thereby; and means so coordinating the operation ofsaid first and second instrumentalities that the latter limit the effectof the former whenever operation of said first instrumentalities tendsto result in either an increase or a decrease in the rate of relativefeeding motion.

25. A machine tool of the type which is characterized by a tool carrier,by regulatable force applying means for effecting relative feedingmotion between the carrier and a workpiece to be cut, and by a cuttingtool on the carrier which is maintained in a normal position withrespect to the carrier as long as feed reaction force on the cuttingtool, which is opposed by an equal biasing force reacting between thecutting edge of the tool and the carrier, is at a predetermined value,said cutting tool being movable relative to the carrier in oppositedirections along the path [[af]] of relative feeding motion under theinfluence one or the other of said forces in correspondence with changesin feed [[reactingl] reaction force, and said machine tool being furthercharacterized by: instrumentalities associated with said force applyingmeans and with the cutting tool, and responsive both to| movement of the23 cutting lool resulting from changes in feed reaction force thereonand to a function of the rate at which relative feeding motion iseffected by the farce applying means to regulate the force effectingsaid relative feeding motion inversely with changes in feed reactionforce from said predetermined value thereof and t0 an extent determinedby the rate at which said relative feeding motion is effected.

References Cited 2,104,258 1/1938 Hunter 83-201.07

JAMES M.

24 Tucker 83-639 Wells et al. 8320L06 Wells 23S-201.06 Crane 143-25Crane 83-201.06 Crane 23S-201.06 Prins. Herman 83-639 Adams. Crane.

FOREIGN PATENTS Australia.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Reissue No. 26,377April 16, 1968 Charles H. Whitmore It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

Column 2, line 3l, "folow" should read l follow Column 8 line 63 "force"in ltallCS should read force n. Column ll, line 6, "hand-up" should readhang-up n. Column 14, line 40, "72" should read 172 Column 20, line 40,"form" should read from Column 22, line 19, "recation" should readreaction line 70, after "influence" insert of Signed and sealed this 2ndday of September i969.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attes-ting @fficerCommissioner of Patents

